Q & A

By C. CLAIBORNE RAY

Published: April 16, 2002

Q. Why do chickens have white meat and dark meat and ducks have only dark meat?

A. Chickens and ducks have different exercise habits and different muscle structures, with differing levels of a dark substance called myoglobin.

Chickens, which are mostly earthbound, with an occasional spurt of flying, have breasts that contain mostly fast-twitch muscle fibers; these contract powerfully for a short hop in the air, but they soon become tired.

Fast-twitch muscle fibers also have relatively small amounts of myoglobin, a protein molecule that stores oxygen to be released when muscles need to contract. Myoglobin is dark red because of its iron content.

Other parts of the chicken that tend to get a more prolonged workout, like the leg and thigh muscles, have more of what are called slow-twitch muscle fibers. These fibers are rich in myoglobin and consequently are a darker color; they are less powerful but capable of sustained effort.

Ducks, which are well-known long-distance fliers, also need more myoglobin-rich muscles and so have predominantly dark meat. Other long-distance travelers, like pigeons and geese, also have mostly dark meat.

In humans, too, there appears to be a genetic difference between the musculature of the best long-distance runners, who have more slow-twitch muscle fibers, and that of the best sprinters, who have more fast-twitch fibers. C. CLAIBORNE RAY